[clang] Reapply "[Clang][Sema] Diagnose function/variable templates that shadow their own template parameters (#78274)" (PR #79683)

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``````````bash
git-clang-format --diff faef68bca852d08511ea0311d8a0d221cb202e73 abc8f062add9e41ce00b9d035c796256a62859ef -- clang/include/clang/Sema/Sema.h clang/lib/Sema/SemaDecl.cpp clang/lib/Sema/SemaTemplate.cpp clang/test/CXX/temp/temp.res/temp.local/p6.cpp
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View the diff from clang-format here.
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``````````diff
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 5c148db481..d0fb4f0991 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -8256,7 +8256,8 @@ public:
                                       TemplateSpecializationKind TSK,
                                       bool Complain = true);
 
-  void DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl, bool IssueWarning = false);
+  void DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl,
+                                       bool IssueWarning = false);
   TemplateDecl *AdjustDeclIfTemplate(Decl *&Decl);
 
   NamedDecl *ActOnTypeParameter(Scope *S, bool Typename,
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index de65b3c09c..2cb971b052 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -6502,22 +6502,23 @@ NamedDecl *Sema::HandleDeclarator(Scope *S, Declarator &D,
 
   // if (Previous.isSingleResult() &&
   //    Previous.getFoundDecl()->isTemplateParameter()) {
-  if (auto *TPD = Previous.getAsSingle<NamedDecl>(); TPD && TPD->isTemplateParameter()) {
+  if (auto *TPD = Previous.getAsSingle<NamedDecl>();
+      TPD && TPD->isTemplateParameter()) {
     // Older versions of clang allowed the names of function/variable templates
-    // to shadow the names of their template parameters. For the compatibility purposes
-    // we detect such cases and issue a default-to-error warning that can be disabled with
-    // -fno-strict-primary-template-shadow.
+    // to shadow the names of their template parameters. For the compatibility
+    // purposes we detect such cases and issue a default-to-error warning that
+    // can be disabled with -fno-strict-primary-template-shadow.
     bool IssueShadowingWarning = false;
     for (Scope *Inner = S; (Inner->getFlags() & Scope::DeclScope) == 0 ||
-         Inner->isTemplateParamScope(); Inner = Inner->getParent()) {
+                           Inner->isTemplateParamScope();
+         Inner = Inner->getParent()) {
       if (IssueShadowingWarning = Inner->isDeclScope(TPD))
         break;
     }
 
     // Maybe we will complain about the shadowed template parameter.
     if (!D.isInvalidType())
-      DiagnoseTemplateParameterShadow(D.getIdentifierLoc(),
-                                      TPD,
+      DiagnoseTemplateParameterShadow(D.getIdentifierLoc(), TPD,
                                       IssueShadowingWarning);
 
     // Just pretend that we didn't see the previous declaration.
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 4ba8dfc19d..2993da99ff 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -885,7 +885,8 @@ bool Sema::DiagnoseUninstantiableTemplate(SourceLocation PointOfInstantiation,
 /// that the template parameter 'PrevDecl' is being shadowed by a new
 /// declaration at location Loc. Returns true to indicate that this is
 /// an error, and false otherwise.
-void Sema::DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl, bool IssueWarning) {
+void Sema::DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl,
+                                           bool IssueWarning) {
   assert(PrevDecl->isTemplateParameter() && "Not a template parameter");
 
   // C++ [temp.local]p4:
@@ -894,10 +895,9 @@ void Sema::DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl, b
   //
   // Make this a warning when MSVC compatibility is requested.
   unsigned DiagId = getLangOpts().MSVCCompat
-      ? diag::ext_template_param_shadow
-      : (IssueWarning
-          ? diag::ext_compat_template_param_shadow
-          : diag::err_template_param_shadow);
+                        ? diag::ext_template_param_shadow
+                        : (IssueWarning ? diag::ext_compat_template_param_shadow
+                                        : diag::err_template_param_shadow);
   const auto *ND = cast<NamedDecl>(PrevDecl);
   Diag(Loc, DiagId) << ND->getDeclName();
   NoteTemplateParameterLocation(*ND);

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https://github.com/llvm/llvm-project/pull/79683